It’s been 40 years since Apollo 17 astronaut Gene Cernan took humanity’s final steps on the Moon, leaving the world with this hope for the future:

CERNAN: As we leave the Moon and Taurus-Littrow, we leave as we came — and God willing, as we shall return: with peace and hope for all mankind.

So far, of course, no one has returned to the Moon at all. And no one is likely to for many years to come. Plans for the next round of human exploration come and go just about as breezily as the seasons.

But after a lengthy hiatus, lunar exploration has returned, with the next round of robotic missions. Over the last few years, orbiting American spacecraft have mapped the Moon in unprecedented detail. They’ve also mapped the composition of its surface, and found evidence of ice at the south pole. And a current mission is measuring the Moon’s gravity field, providing a better look than ever at the Moon’s interior.

Other nations are exploring the Moon, too. An Indian probe, for example, found evidence that water is mixed with the dirt across much of the lunar surface.

The exploration also continues here on Earth, as scientists study the hundreds of pounds of rock and soil remaining from the Apollo missions. Using techniques that didn’t even exist 40 years ago, they’re finding new details about the Moon’s composition, structure, and birth. They’re also helping identify sites for future study — whenever we’re ready to send the next astronauts back to the Moon.